<!doctype html>
<html lang="zh-cn">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>三角形</title>
    <style>
        .box {
            width: 0;
            height: 0;
            float: left;
            border-style: solid;
            margin: 10px;
        }
        .box1 {
            border-width: 100px;
            border-color: tomato transparent transparent transparent;
            transform: rotate(180deg);
        }
    </style>
</head>
<body>
<div class="box box1"></div>
</body>
</html>